The present invention relates generally to braking systems for elevators and, in particular, to an elevator remote brake release with a clutch.
Elevators and their associated mechanical components are well known. Elevators are used to move people and things between floors in multistory buildings. A conventional traction type elevator application includes an elevator car attached to a counterweight via a suspension cable, and a drive machine rotating a traction sheave that is engaged with the cable. As the drive turns the sheave, friction forces between the grooved surface of the sheave and the cable cause the car and counterweight to oppositely raise and lower in a hoistway. A brake associated with the drive is used to slow and stop the car. The drive machine and the brake are typically located in a machine room accessible by maintenance personnel. The machine room can be located at the top or the bottom of the hoistway or adjacent to the hoistway.
Elevators are also provided with control systems that perform various functions for ensuring smooth and safe operation of the elevator including operating the drive machine and the brake. Advances in elevator technology have led to the development of mini-machine-room or machine-room-less (MMR/MRL) elevator applications. As their names imply, these types of elevator mechanical systems employ very small machine rooms or no machine rooms at all. MMR/MRL elevator applications have the goal of reducing the amount of building space occupied by the elevator systems and thereby increasing the amount of usable space on the floors, and are becoming more and more common.
The brake is a major component of the electrical mechanical and control systems. The brake is utilized in normal operation for arresting the movement of the elevator car, but also is engaged in emergency situations in order to prevent the car from moving within the hoistway. Brakes typically utilize a spring or clutch mechanism with accompanying wear plates that engage with a drum area on the drive motor, or alternatively with a cylindrical brake drum that is attached to the suspension cable, in order to stop the movement of the elevator car.
Elevators are provided with numerous safety systems in addition to the basic mechanical components and control systems described above. Safety systems generally contain sensors that monitor the condition of the mechanical components or the operation of the control systems. The safety systems are engaged whenever the mechanical components or control systems are operating in a manner to meet or exceed preset limits for safety, and may utilize the brakes to stop the movement of the elevator car. The safety systems may also stop operation, for example by disconnecting power, of the drive and control system, where feasible.
In emergency situations, the brake is typically engaged so that the elevator car remains stationary in the hoistway. When this occurs, the elevator car may be between floor levels. It is desirable to be able to move the car short distances, for example to the adjoining floor, so that any occupants can exit the car safely and/or maintenance personnel can enter the car. The elevator car is moved by overriding the application of the brake using an emergency brake release. In many prior art systems, the emergency brake release could only be activated from the machine room, making the process both time-consuming and inefficient.
It is especially desirable for the brake release to be actuated remotely so that maintenance personnel can actuate the brake release without having to enter the machine room. Furthermore, in MMR/MRL elevator applications the drive machine and the associated brake are not easily accessible. Prior art patents have recognized this desirability. The U.S. Pat. No. 5,526,902 describes a means for utilizing a brake release from inside the elevator car. The U.S. Pat. No. 5,971,109 describes the remote operation of brake release by utilizing linkage from the interior of the car, or alternatively, from another space adjacent to the elevator shaft but remote from the machinery space.
The prior art noted above, however, does not contemplate the fact that an emergency situation may occur or that the elevator car may move too quickly after the brake release has been engaged. For example, an overspeed condition may occur after the brake has been released, and the prior art shows no way to reengage the brake in order to prevent a catastrophic failure or at least an undesirable condition from occurring.
It is desirable to provide a remote brake release that has the ability to be disengaged, and to reengage the elevator brake if an emergency condition, such as an overspeed condition, is detected.
It is an object of the present invention, therefore, to provide a safe and efficient means of remotely releasing a drive machine brake on applications where the drive machine and the brake are not accessible. It is another object of the present invention to increase the safety of the entire elevator application by integrating the brake release mechanism with an overspeed detection system.
The brake release apparatus according to the present invention provides a safe and efficient means of remotely releasing a drive machine brake on applications where the drive machine and brake are not accessible, which is typical of Machine Room Less (MRL) and Mini Machine Room (MMR) applications. The advantage of this invention over the prior art is that it provides a means of automatically disengaging the remote brake over-ride should an overspeed condition be detected. Once disengaged, the standard return springs on the drive machine brake cause the brake to re-apply thus slowing and stopping the car.
The brake release apparatus according to the present invention includes a solenoid and simple spring clutch to engage or disengage an emergency brake release. A brake release lever is located where it may be accessed by a qualified elevator service technician. Rigidly attached to the brake release lever is a shaft. A spring clutch is fitted around the end of the shaft. A second shaft is also fitted into the spring clutch and is then connected to a bellcrank and from there to a cable. The cable is attached to the brake on the drive machine.
The spring clutch is a simple helical spring made from rectangular spring wire. It is preferably fit to the two shafts with a slight interference fit (approximately 0.1 mm). Pulling down on the brake release causes the brake release lever shaft to rotate. The spring (right hand or left hand) is selected such that pulling down on the brake release lever causes the spring to wind tighter onto the bellcrank shaft thus transmitting torque to the bellcrank. Pushing up on the lever causes the spring to unwind, releasing the spring and preventing torque transmission.
One end of the spring is fastened to the brake release lever shaft. The other end of the spring is free. The free end has a small pad that can be engaged by a solenoid or other similar device. The purpose of this arrangement is that the solenoid can then be used to disengage the clutch should an overspeed condition be detected. It does this by pushing on the pad and unwinding the spring. This clutch and solenoid arrangement is known in the art as a xe2x80x9cnormally engagedxe2x80x9d clutch.
The present invention can be practiced in arrangements other than mechanical actuation of the brake release and electrical actuation upon an overspeed detection. Other arrangements are possible by varying the hand of the spring, the fixation locations (and methods) of the spring to the shafts and the control circuit logic.
In an alternative embodiment, the present invention may also be practiced with a xe2x80x9cnormally disengagedxe2x80x9d device using the same elements. In place of an interference fit, the spring would have a clearance fit to the shaft on the brake release lever. The solenoid would be located on the brake lever side of the spring. To actuate the emergency release, the solenoid would extend and push on the spring tab. This would cause the spring to wind xe2x80x9cdownxe2x80x9d on the brake release shaft. Torque in the shaft would then be transmitted to the brake.
In another alternative embodiment, the present invention makes it possible to eliminate the free rotation that will occur in the brake release lever when the solenoid disengages the clutch. A second spring can be added between the brake lever and ground. This second spring would be xe2x80x9cnormally disengagedxe2x80x9d. The solenoid would actuate both springs, causing the spring between the emergency brake lever and the brake to disengage, and causing the spring between the brake release lever and ground to engage.
Finally, the present invention is not limited to the use of spring clutches. A friction type disc clutch could be used instead of the spring clutch.
The present invention advantageously combines an overspeed protection with the brake release mechanism, providing an additional level of safety with the elevator operation and maintenance.